It is our objective to carry out detailed structure analyses of enzymes by the established techniques of x-ray crystallography. We propose to continue studies of the flavoproteins involved in biological oxidations, already initiated by determination of the crystal structures of all three oxidation states of flavodoxin from Clostridium MP. The structure of flavodoxin from Anacystis nidulans has recently been solved. The molecular conformation of this electron carrier will be refined and compared with the structures of other flavodoxins. Electron microscopy and x-ray diffraction will be used to examine crystals of the complex containing ferredoxin-NADP- reductase and ferredoxin. Preliminary electron density maps of cytochrome c554 from Anacystis nidulans and of iron superoxide dismutase from E. coli will be improved, by the inclusion of additional heavy atom derivative data in the dismutase case, and by model refinement in c554.